Due to the gradual ageing of populations in many countries and regions, most of the elderly need to use a wheel chair as their daily means of transport, but stairs are often obstacles to those in wheel chairs; to bypass such obstacles, they usually have to travel a long distance to reach their destinations; even worse is when there is no other access, the wheel chair must be manually moved, e.g., up and down the stairs, under the assistance by several people.
Electric wheel chair may be able to solve the above problem of moving up and down on stairs, but it is complicated in structure and expensive, and many consumers can not afford it. In addition, when an electric wheel chair goes up and down on stairs, safety is also a big problem.
A Chinese utility model patent (Publication No.: CN2580934Y) disclosed an obstacle-free and self-propelling wheel chair, which is provided with left and right plastic wheels and a multi-directional guiding wheel for travelling on a horizontal plane and climbing a small slope, and also provided with four spider wheels for moving up on stairs. When such wheel chair is used for moving up the stairs, a pull bar needs to be pulled, the right and left plastic wheels and the multi-directional guiding wheel are lifted up accordingly through a connecting rod and under leverage, whilst the seat of the wheel chair is being changed into a reclined position. At that time, the four spider wheels come into contact with the tread of the stairs, and the pull bar needs to be pushed down in order to transmit the driving force to the longitudinal shaft, and through worm gear assemblies to reduce speed, a larger driving force can be exerted to drive a simultaneous rotation of the four spider wheels for an up and down movement on stairs. However, due to varying lengths and widths among different treads of the stairs, the spider wheels are prone to slip over the edge of the treads, resulting in a safety problem. In addition, the structure of a spider wheel is quite complicated, so that the production cost is relatively high.